When Creating a Demand Curve for a Good Where One

When creating a demand curve for a good where one group gets the good for free and another group must pay the market price you must

A) add the quantity demanded for each group at each price.
B) add the price paid at each quantity.
C) take an average of the quantity demanded at each price.
D) add the amount that the first group wants (when it is available to them free) to the quantity demanded by the second group at each price.